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In the weeks after conception, your baby starts out as an embryo made up of three distinct germ layers: the endoderm, mesoderm and ectoderm, all of which form at just 3 weeks gestation. It’s in the last of these “derms” — the ectoderm — where the vast majority of skin, hair and nails develop.

Fetal skin development

Skin — the body’s largest organ — first starts to emerge between week 5 and week 8. At this point, your baby’s epidermis (i.e., skin) consists only of two layers: basal cells (the inner layer of cells) and periderm cells (the outer layer of cells). Hair begins developing immediately after skin, with initial hair buds sewing their seeds after just 8 weeks.

When you’re around 9 weeks or 10 weeks pregnant, something called epidermal stratification begins, or the development of a new intermediate cell layer. This one is right in between the basal and periderm layers, and it’s where your little one’s hair follicles emerge. Over the coming weeks, more stratification occurs. By month 4, all layers of the epidermis are developed and close to adult-quality.

Fingernail and toenail development

Before your baby’s hair starts to actually sprout, something exciting happens: Your baby’s fingernail and toenail beds begin to form at week 11, with the nails themselves starting to grow at week 12. By about 34 weeks, give or take, your little one’s itty-bitty finger- and toenails have will be just about ready for their first postpartum mani and pedi.

Fetal hair development

Around week 14 or week 15, teeny tiny baby hairs start to poke through the skin at a slight angle, with the stage set for your baby’s hairline very soon. Throughout pregnancy, his or her hair actually goes through two cycles of shedding and regrowth. And a precise pattern emerges, with all follicles perfectly and evenly spaced (in fact, not a single follicle forms after birth). Eyelashes and eyebrows are looking pretty good too right around week 22.

Fun fact: Your baby-to-be’s brain is busy with a growth spurt, too, with the delicate skin on little one’s scalp stretching to accommodate her growing brain. And even before hair sprouts, this stretch results in the parietal hair whorl — that clockwise (or counterclockwise) twirl of hair on the back of your head. (More than half of all whorls are located left of the middle of the head, likely because the left side of the brain is a bit larger than the right.)

Lanugo

Hair growth is not limited to baby’s head. At week 14, she’s covered with something called lanugo, a downy coating of hair to keep her warm. Alas, your baby (most likely) will not be sporting her “fur coat” upon birth: As fat accumulates on your baby’s body, it’ll take over the job of keeping her warm — which means the lanugo will shed around week 30.

Vernix caseosa

Come week 19, your baby-to-be’s still-transparent and fragile skin is covered with vernix caseosa (which roughly translates to “cheese varnish” in Latin). This greasy, white layer is made up of shed skin cells and sebaceous secretions, like oil. It protects baby’s skin from amniotic fluid — without it, at birth your little one would look even more wrinkled than she often already does after her 9-month-long acidic bath.

By about week 34, baby-to-be’s protective vernix thickens up, only to be (mostly) shed of couple weeks later. At that point it combines with baby’s departing lanugo in the amniotic fluid; your baby actually swallows the mix, and it becomes the contents of her meconium (or her first poop).

Skin complexion

Up until the very last weeks of pregnancy, your baby has very little body fat, making her skin look transparent. But at around 32 weeks, as your baby steadily fattens up her transparent appearance takes a turn for the opaque. When she’s finally born, she’ll have a reddish-purple complexion, no matter your (or your partner’s) skin color. Her complexion will slowly change to its permanent tone once her circulatory system adjusts to out-of-womb life, a process that can take up to six months for some babies.

As your due date approaches, your hormones make their way through the placenta and amp up the oil production of your baby-to-be’s skin. Your little one will flush out most of these hormones between a week and a month after her birth. But in the meantime, these hormones can lead to cradle cap (scales and flakes on baby’s scalp) and acne in newborns.

Hair color, volume and texture

If you could snap a photo of baby in-utero, you wouldn’t see black curls or blond wisps just yet: Hair is pigment-free and bright white during pregnancy. In fact, all babies — no matter your ethnicity — sport the same thin, silky and often lightly-colored hair at birth, called vellus. Once those first strands sprout in, however, don’t get too attached to what you see: When your newborn is 8 to 12 weeks old, her hair will go through one more phase of development, which often results in one last shedding, with intermediate hair growing in between 3 and 7 months. You’ll actually have to wait till your baby is 2 years old for her “terminal hair” (or the hair she’ll have as a grown-up) to grow.

Wondering whether you’ll give birth to a mop top or a cue ball? That’s genetic. Your chance of having a baby with lots of hair, however, is a bit more predictable. Darker complexions have slower grow-and-shed cycles, which mean a thicker head of hair. Another clue: If you experience a significant amount of heartburn during pregnancy, there really is a good chance you baby-to-be will have a good head of hair. Researchers from Johns Hopkins Medical Institutions have confirmed this pregnancy myth, noting there’s likely a biologic mechanism involving pregnancy hormones that both relaxes the esophageal sphincter and regulates fetal hair growth.

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